1. Field of the Invention
The present invention is broadly concerned with methods and apparatus which provide a two-stage protective function through use of primary and secondary protective devices interconnected by means of an actuating assembly so that the secondary protective device operates in response to operation of the primary device. More particularly, the invention is concerned with such methods and apparatus which preferably make use of a primary protective device including a rupturable element (e.g., a panel or disc) responsive to untoward pressure conditions in a protected building or other structure. The actuating assembly is preferably entirely mechanical and is responsive to element rupture via an elongated cable assembly which effects operation of a secondary protective device upon rupture of the element.
2. Description of the Prior Art
A wide variety of protective devices have been employed in the past to protect buildings, manufacturing facilities, tanks, chambers, and other structures. These devices are intended to quickly terminate or interrupt potentially destructive phenomena, such as conditions conducive to explosions or fires. Additionally, two-stage protective assemblies have been provided wherein a primary protective device operates and, as a result thereof, a secondary protective device is also operated.
For example, U.S. Pat. No. 7,814,924 describes a safety valve actuator for shutting off a gas line when triggered by a seismic event. The actuator includes a housing containing a number of elements which are put into motion to mechanically close a gas valve when an inertial ball is jolted from a pedestal during an earthquake or the like. U.S. Pat. Nos. 6,216,719 and 4,310,012 are directed to protective devices for fluid delivery hoses. These disclosures provide protective assemblies such that if a hose is inadvertently disconnected or severed during use, the forces generated thereby mechanically actuate a shutoff valve.
U.S. Pat. No. 4,299,255 and U.S. Patent Publication No. 2004/0113116 related to manual remote safety valve actuators for emergency shutoff of fluid lines. The '255 patent provides a rotatable cable connected to a remote casing and stopper. The casing is engageable by a crank which causes the cable to rotate so that the stopper is either extended or withdrawn, depending upon the direction of rotation of the crank. The '116 publication describes a remote valve actuator which transmits rotational motion to a remote valve, and includes a continuous-loop drive cable connected to a drive wheel and a driven wheel. The drive wheel is engageable by a crank which, when rotated, drives the cable and causes the driven wheel to rotate. The driven wheel is connected to a valve which is opened or close depending upon the direction of rotation of the driven wheel.
Other references of background interest include U.S. Pat. Nos. 3,788,514, 4,310,012, 4,480,811, 4,523,609, 4,595,374, 4,657,222, 5,461,831, 5,788,212, 6,783,114, and 7,334,773.
While the art discloses the general concept of sequentially operating primary and secondary protective devices using a mechanical linkage, a number of problems remain. First, the art does not recognize the desirability of employing a rupturable burst assembly as a part of the primary protective device and using the explosive forces generated during operation thereof to activate a secondary protective device. Second, the protective assemblies of the prior art are characterized by complex design requiring frequent maintenance and upkeep.